1. Field of the Invention
The present invention is related to capacitors used in integrated circuits, and more particularly, to linear capacitors for use in analog and RF circuits.
2. Related Art
In analog/RF integrated circuits, bias-voltage-independent capacitors are needed to achieve high linearity of circuit performance. However, the bias-voltage-independent capacitors, such as fringe capacitors (made by sidewalling of metal lines), MIM (metal-insulator-metal) capacitors, or poly-oxide-poly capacitors are fairly expensive. These types of capacitors require a large surface area or additional processing steps, leading to higher manufacturing costs. On the other hand, MOSFET-type capacitors have the highest capacitance per unit area, since they are formed by thin gate-oxide, but their capacitance value is dependent on the gate/pickup terminals voltage, and is often non-linear.
Traditionally, circuit designers have chosen Metal-insulator-Metal (MIM) or Poly-insulator-Poly (PIP) based capacitors for bias-independent linear capacitors. However these types of capacitor require a larger area and sometimes require additional fabrication processing steps leading to higher manufacturing costs.